How is the tide formed? Why twice a day?

Tide formation: the tidal force of the moon and the sun on the ocean is the cause of seawater fluctuation. In the non-inertial system, tidal force is the resultant force of four forces, namely, the gravity of the moon and its corresponding inertia, and the gravity of the sun and its corresponding inertia.

The earth and the moon are regarded as particles and the center of the earth is regarded as a non-inertial reference. The gravity of the earth particle by the moon particle is the centripetal force of the earth particle moving around the circumference of the homogeneous center, which is equal to and opposite to the inertial force corresponding to this centripetal force. Therefore, the attraction of the moon particles to the earth particles and this inertia force cancel each other out.

In fact, the earth is very large. On the ground closest to the moon, the orbital radius of an object's circular motion around the center of the earth and the moon is obviously smaller than that of a particle on the earth, so the attraction of the moon to the object will be greater than the corresponding inertial force. These two forces can no longer be offset, and the resultant force is opposite to the gravity of the object on the earth, which makes the gravity of the object obviously smaller.

If the "object" is seawater, then there will be a climax. In the part of the sea farthest from the moon, there will also be a climax. The climax in the morning is called tide, and the climax in the evening is called sunseeker, so there is tide.

There are two kinds of tides: for the same sea, if people face the moon, it is a high tide, and when they face the moon, it is also a high tide, so that people can see the high tide twice a day.

Extended data:

Tidal cycle:

1, semidiurnal tide type: a lunar day has two high tides and two low tides, and the tidal range of the former high tide and low tide is almost the same as that of the latter high tide and low tide, and the time of high tide and low tide is almost equal (6 hours, 12.5 minutes).

2. Diurnal tide type: A lunar day has only one high tide and one low tide. Beibu Gulf in the South China Sea is a typical diurnal tide area in the world.

3. Mixed tidal pattern: there are two high tides and two low tides on some days of 1 month, but the tidal range between the two high tides and low tides is quite different, and the time of high tides and low tides is also different; On other days, there are high tides and low tides.

No matter what kind of tide, there will be a big tide with the largest tidal range within two or three days after the first and fifteenth day of each month in the lunar calendar, when the tide rises highest and falls lowest. Two or three days after August 23rd of the lunar calendar, there is a small tide with the smallest tidal range. At this time, the tide does not rise too high, and it is not too low at the end.

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